If you are a new member and you are looking for help with your water being green, dirty, cloudy, ugly, etc, here's what you need to do:
You need to give us starting information.

1st: The basic layout of your pool.
Is it vinyl, fiberglass, concrete, shotcrete, gunite, tile or plaster?
How many gallons of water do you have?
What kind of filter--Sand, DE, or Cartridge?
Do you have a chlorinator or a Salt-Water Chlorinator?
How about a Nature2 erosion system?
How do you chlorinate, or do you use bromine or bacquacil?
How do you test your water quality?
Which of these questions can you answer and which are a mystery?

2nd: Your current pool's chemistry.
You'll need to tell us what's going on in your water. If you cannot do these tests, take a water sample to a local pool store and have them do them:
FC: This is Free Chlorine--the good stuff that kills viruses, bacteria, algae and is the ONLY thing that safely neutralizes fecal matter.
CC: Combined Chloramines--this tells us you are fighting something.
TC: Total Chlorine. This FC + CC. If it's not, something is measured wrong.
pH: This is just what it was in High School chemistry--the measure of the acidity and alkalinity--1 is acid, 14 is alkaline, 7 is neutral (in the lab), 7.3-7.8 is normal for a pool.
TA: Or T/A, Total Alkalinity, or Alkalinity. This is mis-named and confused with pH. It's not. It's a measure of the buffering of pH. What this means is when set at the right level, your pH will resist bouncing around and will stay pretty consistent. Normal range is 80 to 125ppm. It's easy to raise TA when it's low--you add baking soda--yup, from the kitchen. Lowering it is a pain in the patoot.
CYA: Cyanuric Acid or Stabilizer, or Conditioner. CYA prevents your chlorine from burning off too quickly from sunlight and from dropping to 0. But it works by slowing down your chlorine doing its job. So it's a two-edged sword. Too little is a problem, but so it too much. Normally we like to see 30 to 50 ppm. CYA is closely connected to FC. The correct level of FC is determined by the level of CYA.
CH: CA or Calcium, Calcium Hardness, Hardness. Calcium is necessary for plaster / concrete type pools to keep the water from leaching the calcium from the morter. For those pools, 200 to 400 ppm is best, but for vinyl or fiberglass, you don't care as long as it's below 500ppm.

There are other tests pool stores like to do, but unless they are testing for copper, iron or salt, those other tests are useless.

3rd: Algae--that's probably why you are reading this!
Cleaning up algae is quite simple, but what it's not is easy. Simple, not easy. Mostly you need 3 things--a good test kit, lots and lots and lots of liquid chlorine, usually in the form of bleach, and P.O.P.P That stands for POOL OWNER PATIENCE AND PERSISTENCE!

Forget the pucks, the bags of chlorine mis-labled "Shock" the algaecides, clarifiers, flocculants and snake oil sold to you by pool stores. You need lots of bleach--pool stores will swear up and down it will hurt your pool and then sell you the same darn thing labled "Liquid Chlorine" or "Liquid Shock". It's all Sodium Hypochlorite Solution--Laundry bleach.

What you need to do is figure out how much CYA you have in your water, read off the "Best Guess" table the shock level (http://www.poolforum.com/pf2/showthread.php?t=365), then shock your pool to that level--and keep it there. That means add enough chlorine so that when you test your chlorine, you get that shock level as your reading.

Before that you'll want to get your pH to the 7.3-7.8 range. If it's higher, you add acid--muriatic acid (be VERY careful--this stuff has NASTY fumes!) or dry acid sold at pool stores. If it's lower, you raise it with 20 Mule Team Borax from the grocery store.

So your pH is good, and you've added lots of bleach so your pool is at shock level. Now what? You test your pool 3 times a day--if that chlorine level drops, you raise it back to that shock level. Morning, dinner time and bed time will be fine.

Then you have to brush that pool everyday--sides, walls, bottom, stairs. This knocks algae loose so it can't bed in and lets more chlorine get at it--and kill it.

Every day you need to vacuum your pool and you want to dump that vacuumed up water to a drain.

Now you add the P.O.P.P because without it, you'll never get past the algae. You may be at this for a week, or even two weeks, but eventually, the algae will die, and you'll get that dead algae out and your water will sparkle. It's a very simple process. Simple, but not easy.

Now, you are fine. Unless, of couse, something ELSE is causing cloudy water...
Carl.